It is well known that shampoos, to be marketable, must meet certain stringent requirements in addition to their necessary detergent properties. These requirements are to some degree dependent on which of the two major areas of application they are to be used in. In one area, i.e., for baby shampoos, it is desirable that they have outstanding clarity, a controlled range of viscosity, extremely low irritability, and rapid foaming. In contrast, for adult formulations, opaque (even pearlescent) properties are favored, high viscosity is preferred, mildness (while still necessary) is a less stringent requirement, and conditioning qualities are sought.
It is well known that shampoos not irritating to the eyes can be formulated with certain ratios of ethoxylated anionic and amphoteric detergents in combination with other highly ethoxylated ingredients. Systems of this type are usually thickened with high molecular weight ethoxylated esters such as PEG 6000 distearate or PEG 80 sorbitan stearate. See U.S. Pat. No. 4,177,171. The use of the high molecular weight ethoxylated esters is especially desired in baby shampoos because of the importance of viscosity control and irritation reduction.
To achieve the desired viscosity, mild shampoos have been thickened with gums and polymers. In recent years cationic polymers, and especially cationic cellulosic gums, have been popular because they provide conditioning properties as well as viscosity. See U.S. Pat. No. 3,962,418. Unfortunately, the cationic polymers and gums are perceived as having irritation potential and are generally avoided in formulating very mild baby shampoos.
In yet another approach, U.S. Pat. No. 4,426,310 teaches that a mild shampoo can be thickened by selecting an optimum ratio of anionic and amphoteric detergents. Shampoos of this type usually contain high levels of ethoxylated nonionics such as Polysorbate 20 to achieve low irritation scores.
One drawback of formulations dependent on ethylene oxide derivatives is that these derivatives often contain 10 or more ppm of 1,4-dioxane, an impurity which has been identified as a carcinogen. Another drawback is dependence upon the use of PEG 6000 DS, an expensive ethoxylate-containing ester that is troublesome to both manufacture and handle because of its inherent high viscosity.
More recently, in U.S. Pat. No. 5,130,056, it is taught that C.sub.8 -C.sub.18 fatty acid monoesters of diglycerol and/or C.sub.8 -C.sub.16 fatty acid diesters of tetraglycerol are useful for washing agents, cleaning agents, and toiletries, including shower preparations, bubble bath preparations, liquid hand cleansers, and hair shampoos. While these materials meet dermatological and toxicological requirements and, further, are biodegradable, they have not been found satisfactory for building broad viscosity ranges to the extent desirable for commercial formulations.
In light of the foregoing, it is obviously desirable to formulate baby shampoos which are entirely free of ethylene oxide derivatives and adult shampoos devoid of high molecular weight ethoxylated esters.